This invention relates to abrasive discs for rotary sanders or double action sanding machines and in particularly to a system for removably securing the abrasive discs to the backup pad of such machines.
Conventionally, abrasive sheets or sanding discs are bonded by adhesive, known in the trade as a feathering adhesive, to backup pads or backup plates of sanding machines and while this method has been in use for sometime it has a number of drawbacks. For one, the operator has to apply the adhesive or glue both to the disc and to the backup pad. In many cases, the operator applies the glue to the paper and rubs both the disc and the backup pad together so as to spread the adhesive evenly on the paper. However, in many cases the glue or adhesive gets onto the abrasive side of the disc and subsequently gets onto the paint surface of sheet metal which is being sanded. It also plugs up the sanding disc. Moreover, the sandpaper in many cases tears up in use and when the operator tries to remove the sandpaper from the backup pad it pulls away in small pieces or chunks.
It is often impossible for the operator to remove the sanding disc completely from the backup pad because of the chunks or pieces of paper left adhered to the backup pad from the previous disc. The operator then has no other choice but to apply more glue on top of the old sanding disc pieces and this causes high spots on the backup pad and presents an uneven and unbalanced operative surface. It will be appreciated that when the operator applies the second or new sandpaper disc on the high spots alone, the rest of the disc does not even touch the sanded surface. This leads to the high spots creating plugging up of the sandpaper which in turn leaves marks on the surface being sanded. Additionally, this can result in ripped sandpaper discs and if the operator does not immediately catch it, the existing glue on the backup pad will stick to the paint on the surface being sanded which in turn has to be resanded and repainted again.
The above-mentioned problems are compounded when an operator is using a fine sandpaper disc as the finer papers are the most critical to be used with a glue-on system. The finer papers bond so strongly to the backup pad that the paper tears when it is being removed therefrom. Furthermore, the fine paper tears very easily when it is in use and then the feathering adhesive on the backup pad is rubbed into the paint of the surface being sanded and the glue stays on the sanded surface, the backup pad becoming dirty and dusty from the paint. In a situation of this sort, the operator then has great difficulty in removing the ripped sandpaper from the backup pad because the backup pad is dirty and there are chunks of ripped and split sandpaper. The operator is then normally forced to apply more adhesive to the backup pad to make the next disc stick and if the paper is strong enough to be peeled away from the pad, the paper takes a lot of the feathering adhesive from the backup pad.
In another example of conventional glue-on systems, the manufacturer of the sanding disc applies glue to the sanding disc so that the operator does not have to do it. However, the problem remains exactly as defined above. The paper tears, the pad gets dirty and more glue must be applied to the backup pad.
In another example of the prior art, a manufacturer applied glue to the sanding disc and then applies a wax paper over the glue. The operator has to remove the wax paper but this method does not change any of the above-mentioned problems which appears subsequent to putting the paper on to the backup pad. Wax paper is added to the back of the sanding disc only so that the glue will not dry out and that one disc will not stick to another.
One of the main problems therefore with previously available glue-on or stick-on discs is the removal of the discs from the backup pad when the disc is worn out. Even using strong rosin paper, it has been found that it is almost impossible to remove the disc cleanly from the backup pad and in some cases operators have had to heat the papers in an attempt to soften the adhesive to completely remove the disc.